Four different plots? One for each girl and then a threesome?
Kyon individually with each girl and then with the three of them at once (foursome) was just one of the plots.
After that there was Sasaki trying to get ahead of Haruhi by hiring him, and a comedic series of lemon-flavored events and competitions between Haruhi and Sasaki with a WAFFy ending.
Then there's a crossover with Kyon and any girl/woman in a relatively normal, present day setting. I was thinking of Ami Mizuno's mother after some lemon from a few years ago had that plot with Ranma.
Then there was the idea where Haruhi would watch Ouran Host Club and then dream the SOS-dan as a host club (and discreet escort service) with Kyon actually living out these events as a result of her dreams.